Limiting electronic package warpage

ABSTRACT

An electronic package includes a carrier, semiconductor chip, a lid, and a lid-ring. The carrier includes a top surface and a bottom surface configured to be electrically connected to a system board. The semiconductor chip is electrically connected to the top surface. The lid is attached to the top surface enclosing semiconductor chip and includes a perimeter recess. The lid-ring is juxtaposed within the perimeter recess. The lid-ring exerts a reverse bending moment upon the lid to limit warpage of the electronic package.

FIELD OF THE EMBODIMENTS

Embodiments of the present invention generally relate to electronicdevices and more specifically to limiting warpage within electronicdevice packages.

DESCRIPTION OF THE RELATED ART

An electronic package may include an integrated circuit (IC) chip,semiconductor die, processing module, and the like, packaged onto acarrier or substrate. The package may be encapsulated by a cover havinghigh thermal conductivity. Flatness of the package is important toensure reliable higher level device packaging. For example, it isimportant that the carrier be flat to ensure a reliable electricalconnection with a system board and it is important that the cover beflat to ensure a reliable thermal connection with a heat spreader, suchas a heat sink.

Known techniques to reduce package warpage are to utilize a thick coverand to utilize a carrier having a low coefficient of thermal expansion(CTE). A disadvantage in utilizing the thick cover is the overallincrease in package thickness and the potential benefits of the low CTEcarrier are limited because of the relative large percentage of coppertherein.

SUMMARY

In an embodiment of the present invention, a method to fabricate anelectronic package includes electronically coupling a semiconductor chipto a carrier, attaching a lid to the carrier to enclose thesemiconductor chip, the lid comprising a perimeter recess, and attachinga lid-ring to the perimeter of the lid within the perimeter recess.

In another embodiment of the present invention, an electronic packageincludes a carrier, a semiconductor chip, a lid, and a lid-ring. Thecarrier includes a top surface and a bottom surface configured to beelectrically connected to a system board. The semiconductor chip iselectrically connected to the top surface. The lid is attached to thetop surface enclosing the semiconductor chip and includes a perimeterrecess. The lid-ring is juxtaposed within the perimeter recess.

In yet another embodiment, a method includes electrically connecting anelectronic package to a system board, the electronic package comprisinga carrier including a top surface and a bottom surface configured to beelectrically connected to the system board, a semiconductor chipelectrically connected to the top surface, a lid attached to the topsurface that encloses semiconductor chip, the lid having a perimeterrecess, and a lid-ring within the perimeter recess and thermallyattaching a heat sink to the electronic package with a thermal interfacematerial there between.

These and other embodiments, features, aspects, and advantages willbecome better understood with reference to the following description,appended claims, and accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES

So that the manner in which the above recited features of the presentinvention are attained and can be understood in detail, a moreparticular description of the invention, briefly summarized above, maybe had by reference to the embodiments thereof which are illustrated inthe appended drawings.

It is to be noted, however, that the appended drawings illustrate onlytypical embodiments of this invention and are therefore not to beconsidered limiting of its scope, for the invention may admit to otherequally effective embodiments.

FIG. 1 depicts an electronic device utilizing a prior art electronicpackage.

FIG. 2-FIG. 7 depict exemplary electronic packages, according to one ormore embodiments of the present invention.

FIG. 8 depicts a method for fabricating an electronic package, accordingto one or more embodiments of the present invention.

FIG. 9 depicts a method for installing an electronic package into anelectronic device, according to one or more embodiments of the presentinvention.

FIG. 10 depicts a block diagram of an exemplary electronic device thatutilizes a electronic package, according to one or more embodiments ofthe present invention.

DETAILED DESCRIPTION

FIG. 1 depicts a prior art electronic device 100 utilizing electronicpackage 124. Electronic device 100 may be, for example, a computer,server, mobile device, tablet, and the like. Electronic package 124includes IC chip 102, carrier 108, interconnects 122, underfill 110,thermal interface material 112, lid 116, and adhesive 120. Chip 102 maybe an integrated circuit, semiconductor die, processor, microchip, andthe like. Carrier 108 may be an organic carrier or a ceramic carrier andprovides mechanical support for chip 102 and electrical paths from theupper surface of carrier 108 to the opposing side of carrier 108.Interconnects 122 electrically connect chip 102 and the upper side ofcarrier 108 and may be a wire bond, solder bond, stud, conductive ball,conductive button, and the like. Underfill 110 may beelectrically-insulating, may substantially surround interconnects 122,may electrically isolate individual interconnects 122, and may providemechanical support between chip 102 and carrier 108. Underfill 110 mayalso prevent damage to individual interconnects 122 due to thermalexpansion mismatches between chip 102 and carrier 108.

When chip 102 is seated upon carrier 108, a reflow process may beperformed to join interconnects 122 to electrical contacts of both chip122 and carrier 108. After chip 102 is seated to carrier 108 a lid 116is attached to carrier 108 with adhesive 120 to cover chip 102.Generally, during operation of electronic device 100, heat needs to beremoved from chip 102. In this situation, lid 116 is both a cover and aconduit for heat transfer. As such, a thermal interface material 112 maythermally join lid 116 and chip 102.

Electronic package 124 may be connected to a system board 106 viainterconnects 114. System board 106 may be the main printed circuitboard of electronic device 100 and includes electronic components, suchas a graphics processing unit, memory, and the like, and providesconnectors for other peripherals. Interconnects 114 electrically connectthe lower side of carrier 108 to system board 106 and may be a wirebond, solder bond, stud, conductive ball, conductive button, and thelike. Interconnects 114 may be larger and thus more robust thaninterconnects 122. When electronic package 124 is seated upon systemboard 106 a second reflow process may be performed to join interconnects114 to electrical contacts of both carrier 108 and motherboard 106.

To assist in the removal of heat from chip 102 a heat sink 104 may bethermally joined to electronic package 124 via thermal interfacematerial 118. Heat sink 104 may be a passive heat exchanger that coolschip 102 by dissipating heat into the surrounding air. As such, duringoperation of electronic device 100, a thermal path exists from chip 102to heat sink 104 through thermal interface material 112, lid 116, andthermal interface material 118, and the like. Heat sink 104 may beconnected to system board 106 via one or more connection device 130.Connection device 130 may include a threaded fastener 132, standoff 134,backside stiffener 136, and fastener 138. Threaded fastener 132 mayextend through heat sink 104, standoff 134, and backside stiffener 136and provides compressive force between heat sink 104 and backsidestiffener 136. The length of standoff 134 may be selected to limit thepressure exerted upon electronic package 124 by heat sink 104 created bythe compressive forces. Backside stiffener 136 may mechanically supportthe compressive forces by distributing the forces across a larger areaof motherboard 104. In other applications, connection device 130 may bea clamp, non-influencing fastener, cam, and the like, system thatadequately forces heat sink 104 upon electronic package 124.

Thermally connected, joined, and the like, shall herein mean thatelements that which are thermally connected are able to efficientlytransfer heat there between (e.g., air gaps between the elements areminimized). Electrically connected, and the like, shall herein mean thatcurrent is able to be efficiently passed from one element to anotherelement (e.g., current flows from a conductor in one element to aconductor in the other element).

FIG. 2 depicts an exemplary electronic package 200 according to variousembodiments of the present invention. Electronic package 200 may includeIC chip 202, carrier 208, interconnects 222 (not shown), underfill 210,thermal interface material 212, lid 250, and seal band 220.

Carrier 208 provides a base on which the chip 202 is mounted andelectrically connected thereto via a plurality of interconnects (e.g.solder, pillars, wire bonds, and the like). Carrier 208 may be composedof ceramics or organic materials. If organic, carrier 208 may includemultiple layers of metallization and dielectric materials. Dependingupon the configuration of layers, carrier 208 may be a coreless, thincore, or standard core design. The dielectric materials may be, forexample, epoxy resin with or without fiberglass fill. In variousembodiments, carrier 208 may interconnect with other devices such as asocket (pin grid array, land grid array, ball grid array, and the like).In various embodiments, carrier 208 may include other devices besideschip 202, for example, surface mount devices (e.g. capacitors,resistors, and the like).

Chip 202 may be for example a microchip, microprocessor, graphicprocessor, combined processor and graphics processor, applicationspecific integrated circuit (ASIC), system on a chip (SOC), threedimensional integrated circuit, system on insulator (SOI), and the like.

Lid 250 encapsulates the chip 202. The underside of lid 250 isconfigured to make thermal contact with chip 202 and contact withcarrier 208. Therefore, lid 250 may include an underside cavity of adepth of approximately the height of chip 202. The upper side of lid 250further includes a perimeter recess 255. Recess 255 generally acceptslid-ring 260, as is depicted in FIG. 3 to limit warpage of electronicpackage 200. Lid 250 may be mechanically fastened to carrier 208 by sealband 220. Seal band 220 is generally an adhesive and may be thermallycompliant such that it may adsorb dimensional fluctuations of lid 250and/or carrier 208 due to thermal expansion. Lid 250 may be made from athermally conductive material, such as a metal. For example, lid 250 maybe formed (e.g., milled, cast, and the like) from copper.

Electronic package 200 may include thermal interface material 212 layersjuxtaposed between chip 202 and covers 204. Thermal interface material212 generally reduces air gaps between chip 202 and lid 250, therebyincreasing heat transfer away from chip 202. Thermal interface material212 may be a thermal gel, thermal compound, thermal paste, heat paste,and the like. In an embodiment, the thickness of thermal interfacematerials 212 is generally minimized. In certain embodiments, thermalinterface material 212 is composed of metallic materials, such assilicone rubber mixed with aluminum and zinc oxide. Other compliant basematerials other than silicone rubber and thermally conductive materialsmay be used.

FIG. 3 depicts an exemplary electronic package 200 according to variousembodiments of the present invention. Electronic package 200 may furtherinclude lid-ring 260. Lid-ring 260 may be juxtaposed fit with theperimeter recess 255 of lid 250. For example, lid-ring 260 may laywithin perimeter recess 25. In some embodiments, lid-ring 260 may bepress-fit, interference fit, and the like, into perimeter recess 255. Inother embodiments, lid-ring 260 may be fastened to lid 250 via afastener (e.g., adhesive, seal band, and the like). Lid-ring 260 may bemade from a thermally conductive material, such as a metal. In anembodiment, lid 250 and lid-ring 260 are similar metals. In anotherembodiment, lid 250 and lid-ring 260 are different metals. For example,lid-ring may be formed (e.g., milled, cast, and the like) from aluminum.

In an embodiment, recess 255, and corollary, cover-lid are arranged uponthe upper half of lid 250. For example, a plane that bisects the heightof lid-ring 260 may be above a plane that bisects the height of lid 250.

Lid-ring 260 generally creates a compressive force upon and from theperimeter of lid 250 inward, as depicted by the arrows of FIG. 3. Suchcompressive force aids in limiting warpage of electronic package 200.More particularly, the compressive force exerted by lid-ring 260 uponlid 250 helps to maintain flatness of the electronic package 200. Forinstance, the lid-ring 260 helps to maintain an upper surface 251 of lid250, an upper surface of carrier 208, and the like, to be parallel withflat plane 252. The compressive force may be generated by the greatercontraction of lid-ring 260 relative to lid 250. The contraction oflid-ring 260 exerts a reverse bending moment upon lid 250 to aid inflattening the electronic package 200. For clarity, the convex warpageof electronic package 200 to be prevented may be caused by coefficientof thermal expansion mismatches between the various components of theelectronic package 200.

Referring to FIG. 4-FIG. 7 simultaneously, which depict exemplaryarrangements of lid-ring 260 upon lid 250. Lid-ring 260 may be fastenedto lid 250 a seal band 270. The seal band 270 may be similar to the sealband 220 or may be a different material type configured for metal tometal bonding. The seal band may be upon a single recess 255 surface orupon multiple recess 255 surfaces. For example, seal band 270 may beupon a lower recess 255 surface as shown in FIG. 4, may be upon thelower recess 255 surface and a side recess surface as shown in FIG. 5,and/or may be upon multiple lower recess 255 surfaces as shown in FIG.6. In some embodiments, the upper surface 251 of lid 250 is coplanarwith an upper surface 261 of lid-ring 260.

The seal band 270 and the seal band 220 may be cured at differenttemperatures. For example, seal band 270 may be cured at a highertemperature. The higher curing temperature allows for lid-ring 260 beheated and cooled from the higher temperature resulting in thecontraction of lid-ring 260 relative to lid 250.

As shown in FIG. 4 and FIG. 7, lid-ring 260 may be generally horizontal(i.e., width of lid ring 260 greater than height of lid-ring 260). Asshown in FIG. 5, lid-ring 260 may be generally vertical (i.e. lid-ringheight is greater than lid-ring width). As shown in FIG. 6, lid ring mayinclude a generally horizontal portion 263 and a generally verticalportion 265. For clarity, the recess 255 of lid 250 and an associatedlid-ring 260 may take upon a variety of geometries such that thelid-ring 260 may juxtapose with the recess 255 of lid 250.

Interconnects 222 electrically connect chip 202 and carrier 208 and maybe a wire bond, solder bond, stud, conductive ball, conductive button,and the like. In certain embodiments interconnects 222 may be solderjoints composed of lead, lead-free, or a combination material. Underfill210 may be electrically-insulating, may substantially surroundinterconnects 222, may isolate individual interconnects 222, and mayprovide mechanical support between chip 202 and carrier 208. Underfill210 may also prevent damage to individual interconnects 222 due tothermal expansion mismatches between chip 202 and carrier 208. Incertain embodiments, known epoxy or other resins may be used forunderfill 210.

When chip 202 is seated upon carrier 208, a reflow process may beperformed to join interconnects 222 to electrical contacts of chip 202and carrier 208. After chip 202 are seated to carrier 208, lid 250 isattached to carrier 208 via seal band 220 and thermally attached to chip202 via thermal interface material 212. In some applications, electronicpackage 200 may be connected to a system board.

To assist in the removal of heat from chip 202 a heat sink may bethermally joined to electronic package 200 via compliant thermalinterface material applied to the upper surface 251 of lid 250 and/or tothe upper surface 261 of lid-ring 260. The heat sink may be a passiveheat exchanger that cools chip 202 by dissipating heat into thesurrounding air (such as a pin heat sink, electronic system chassis, andthe like). Heat sink may also be an active heat exchanger (i.e. forcedair, forced liquid cooling system, and the like). As such, duringoperation of the electronic device, a thermal path exists from chip 202to the heat sink through thermal interface material 212, lid 250, andthe like.

FIG. 8 depicts a method 400 for fabricating an electronic package 200,according to various embodiments of the present invention.

Method 400 begins at block 402 and continues with attaching chip 202 tocarrier 208 (block 404). In certain embodiments chip 202 are attachedusing a flip-chip solder bump processes including a solder reflow.Method 400 may continue by dispensing underfill 210 around the perimeterof chip 202 at an ambient temperature (block 406). The underfill 210 maybe drawn under the chip between the chip 202 and carrier 208 bycapillary action. In some embodiments, underfill 210 may be subject tocuring at an elevated temperature (block 408). The curing of underfill210 may or may not coincide with the curing of seal band 220 and/orthermal interface material 212.

Method 400 may continue with dispensing thermal interface material 212upon the top surface of chip 202 and dispensing seal band 220 upon thetope surface of carrier 208 generally around the perimeter of chip 202at the ambient temperature (block 410). Method 400 may continue withaligning lid 250 with the chip 202 and seal band 220 and thermallyattaching the lid 250 with the thermal interface material 212 upon thetop surface of chip 202 and contacting seal band 220 (block 412). Method400 may continue by curing the thermal interface material 212 and/orseal band 220 at an elevated temperature T(1) (block 414). T(1) may be,for example, between 100 degrees Celsius to 165 degrees Celsius. Method400 may continue by cooling the electronic package to the ambienttemperature (block 416).

Method 400 may continue with dispensing seal band 270 within recess 255of lid 250 (block 418) and may continue with aligning and attachinglid-ring 260 with lid 250 (block 240). For example, lid-ring 260 may bejuxtaposed with recess 255 of lid 250. Method 400 may continue withcuring seal band 270 at an elevated temperature T(2) (block 422). T(2)may be, for example, higher relative to T(1) but below solder meltingtemperature (e.g. 275 degrees Celsius). Method 400 may continue bycooling the electronic package to the ambient temperature (block 424).The cooling from T(2) allows for the lid-ring 260 to create acompressive force upon and from the perimeter of lid 250 inward thataids in limiting warpage of the electronic package. Method 400 ends atblock 426.

FIG. 9 depicts a method 500 for installing an electronic package 200into an electronic device according to various embodiments of thepresent invention. Method 500 begins at block 502 and continues withelectrically attaching electronic package 200 to a system board (block504). For example, an array such as a land grid array, ball grid array,and the like, may be attached to the carrier at a reflow temperature.The electronic package may be aligned with the system board and heatedto reflow the array to electrically connect the electronic package withthe system board.

A thermal interface material is applied to electronic package 200 (block506). For example, thermal interface material may be injected, painted,spread, or otherwise applied to the top surface 251 of lid 250. A heatspreader, such as a heat sink, and the like, may be attached toelectronic package 200 (block 508). For example, heat sink may beattached utilizing thermal interface material, thermal tape, epoxy,clip(s), stand offs, and the like. Generally, a force may be applied tosecure heat sink to electronic package 200. In another example, aconnection device 130 may be utilized to attach heat sink.

FIG. 10 depicts a block diagram of an exemplary electronic device 300that may utilize an electronic package 200 according to an embodiment ofthe present invention. It should be appreciated that FIG. 10 providesonly an illustration of one implementation of an embodiment of thepresent invention and does not imply any limitations with regard to theenvironment in which different embodiments may be implemented.

Electronic device 300 includes communications bus 552, which providescommunications between electronic package(s) 200, memory 556, persistentstorage 558, communications unit 560, and input/output (I/O)interface(s) 562. Memory 556 may be, for example, one or more randomaccess memories (RAM) 564, cache memory 566, or any other suitablenon-volatile or volatile storage device. Persistent storage 558 caninclude one or more of flash memory, magnetic disk storage device of aninternal hard drive, a solid state drive, a semiconductor storagedevice, read-only memory (ROM), EPROM, or any other computer-readabletangible storage device that is capable of storing program instructionsor digital information.

The media used by persistent storage 558 may also be removable. Forexample, a removable hard drive may be used for persistent storage 558.Other examples include an optical or magnetic disk that is inserted intoa drive for transfer onto another storage device that is also a part ofpersistent storage 558, or other removable storage devices such as athumb drive or smart card.

Communications unit 560 provides for communications with otherelectronic devices. Communications unit 560 includes one or more networkinterfaces. Communications unit 560 may provide communications throughthe use of either or both physical and wireless communications links. Inother embodiments, electronic device 200 may be devoid of communicationsunit 560. Software may be downloaded to persistent storage 558 throughcommunications unit 560.

I/O interface(s) 562 allows for input and output of data with otherdevices that may be connected to electronic device 200. For example, I/Ointerface 562 may provide a connection to external devices 568 such as acamera, mouse, keyboard, keypad, touch screen, and/or some othersuitable input device. I/O interface(s) 562 also connects to display570.

Display 570 provides a mechanism to display data to a user and may be,for example, a computer monitor. Alternatively, display 570 may beintegral to electronic device 200 and may also function as a touchscreen.

The accompanying figures and this description depicted and describedembodiments of the present invention, and features and componentsthereof. Those skilled in the art will appreciate that any particularprogram nomenclature used in this description was merely forconvenience, and thus the invention should not be limited to use solelyin any specific application identified and/or implied by suchnomenclature.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

References herein to terms such as “vertical”, “horizontal”, and thelike, are made by way of example, and not by way of limitation, toestablish a frame of reference. The term “horizontal” as used herein isdefined as a plane parallel to the conventional plane or surface of thecarrier 208, regardless of the actual spatial orientation of the carrier208. The term “vertical” refers to a direction perpendicular to thehorizontal, as just defined. Terms, such as “on”, “above”, “below”,“side” (as in “sidewall”), “higher”, “lower”, “over”, “beneath” and“under”, are defined with respect to the horizontal plane. It isunderstood that various other frames of reference may be employed fordescribing the present invention without departing from the spirit andscope of the present invention.

1. A method to fabricate an electronic package comprising: electronically coupling a semiconductor chip to a carrier; attaching a lid to the carrier to enclose the semiconductor chip, the lid comprising a perimeter recess, and; attaching a lid-ring to the lid within the perimeter recess, wherein a perimeter sidewall of the lid-ring is coplanar with a perimeter sidewall of the lid.
 2. The method of claim 1, wherein the lid is in thermal contact with the semiconductor chip.
 3. The method of claim 1, wherein a top surface of the lid and a top surface the lid-ring are coplanar.
 4. The method of claim 1, wherein the lid and the lid-ring are the same material.
 5. The method of claim 1, wherein the lid is fabricated from copper and the lid-ring is fabricated from aluminum.
 6. The method of claim 1, wherein attaching the lid to the carrier further comprises: curing a first seal band at a predetermined first elevated temperature.
 7. The method of claim 6, wherein attaching the lid-ring to the perimeter of the lid further comprises: curing a second seal band at a second elevated temperature, the second elevated temperature greater than the first predetermined elevated temperature.
 8. The method of claim 7, further comprising: cooling the electronic package from the second elevated temperature.
 9. The method of claim 1, further comprising: contracting the lid-ring relative to the lid to exert a reverse bending moment upon the lid. 10.-15. (canceled)
 16. A method comprising: electrically connecting an electronic package to a system board, the electronic package comprising a carrier including a top surface and a bottom surface configured to be electrically connected to the system board, a semiconductor chip electrically connected to the top surface, a lid attached to the top surface that encloses semiconductor chip, the lid having a perimeter recess, and a lid-ring within the perimeter recess such that a perimeter sidewall of the lid-ring is coplanar with a perimeter sidewall of the lid; thermally attaching a heat sink to the electronic package with a thermal interface material there between.
 17. The method of claim 16, wherein the lid is in thermal contact with the semiconductor chip.
 18. The method of claim 17, wherein a top surface of the lid and a top surface the lid-ring are coplanar.
 19. The method of claim 17, wherein the lid is fabricated from copper and the lid-ring is fabricated from aluminum.
 20. The method of claim 17, wherein the lid-ring exerts a reverse bending moment upon the lid. 